1. Field of the Invention
The present invention relates to a numerical control device, and more particularly to a numerical control device which smoothly changes feed rate when high-speed cycle machining is stopped.
2. Description of the Related Art
The present invention relates to a numerical control device, and more particularly to a numerical control device which smoothly changes feed rate when high-speed cycle machining is stopped.
In numerical control device (CNC), a high-speed cycle machining technique for performing cycle operation repeatedly. For performing high-speed cycle machining, machining configuration is converted into high-speed cycle machining data and stored in a variable region of the numerical control device, the high-speed cycle machining data is called by an NC program command, and movement amount of command data at each execution cycle is read out from the high-speed cycle machining data for performing the high-speed cycle machining.
FIG. 8 is a diagram illustrating an example of high-speed cycle machining data in prior art. As shown in FIG. 8, the high-speed cycle machining data consist of header and movement amount, and in the header, repetition number of the cycle, data number of the movement amount, and start number of the movement amount are defined, and a number of the movement amounts corresponding to the number designated at the header are prepared for each axis.
FIG. 9 shows a relationship between the movement amount and cycle data for a cycle generated by aggregating a plurality of movement amounts, using a graph of movement amount of control axis of machining tool and time.
As a prior art related to the high-speed cycle machining above mentioned, a technique in which movement amount of the high-speed cycle machining repeating the same operation in cycle operation and NC program command are superimposed (for example, Japanese Patent Laid-Open No. 2010-009094).
Any one of resetting, feed holding, and interlocking is performed during the high-speed cycle machining, execution of the high-speed cycle machining is interrupted, and the drive axis stops immediately at the interruption of the execution since the high-speed cycle machining faithfully implements motion in the command and does not perform acceleration and deceleration by interpolation. Therefore, one of the two methods below is necessary for restraining mechanical shock of the machine or machining error.
Method 1: The high-speed cycle machining data for decelerating and stopping is prepared, the machine set to be state of resetting, feed holding, or interlocking after decelerating and stopping by execution of the cycle.
Method 2: The machine set to be state of resetting, feed holding, or interlocking after decelerating and stopping while the override is decreased little by little using ladder program.
FIG. 10 shows a graph of velocity and time when the high-speed cycle machining data for decelerating and stopping according to Method 1.
The override in Method 2 is function to change feed rate based on the designated magnification of the commanded feed rate by input signal. Actual override for obtaining actual feed rate is calculated by multiplying the commanded feed rate by the designated override by the input signal, and calculates the feed rate by multiplying the commanded feed rate by the actual override. Period for change the actual override by the override is input period of the signal (for example, 4 msec) and is longer than the interpolation period (for example, 1 msec).
It is necessary to prepare a large amount of high-speed cycle machining data for decelerating and stopping from the feed rate at each machining or at acceleration or deceleration, in addition to decelerate and stop while keeping synchronization between each axis when the high-speed cycle machining data for decelerating and accelerating by Method 1 is executed. Therefore, there has been a problem that data size for the high-speed cycle machining data increases and work load for generation of the high-speed cycle machining data increases.
When the ladder program decreases the override little by little in Method 2, capacity for the high-speed cycle machining data is decreased since the high-speed cycle machining data for decelerating and stopping is not necessary, and the work load for generation of the high-speed cycle machining data is decreased. However, since the period for change the actual override by the override is the input period of the signal (for example, 4 msec) and is longer than the interpolation period (for example, 1 msec), there is a program that time and distance necessary for deceleration become long, or change amount for one override become large, and the work load for generating ladder program increases.
FIGS. 11A and 11B shows examples in which the high-speed cycle machining data for decelerating and stopping is executed and in which the override is changed, while the feed rate is changed for the same amount at each step in both examples.
For a gear grinder and a crank pin grinder, there has been a problem that long time is necessary for restarting operation since recovery to start position while a grindstone and a workpiece is synchronized for preventing interference is required when the high-speed cycle machining is interrupted in the cycle operation.